MPG Calculator
Work out your real fuel economy.
Add a price to also see cost per mile.
Results update as you type.
How it works
Your car's window-sticker MPG is an estimate, but the number that matters is the one you actually achieve, and this MPG calculator gives it to you from two figures you can read off at the pump. Enter the miles driven on a tank and the gallons it took to refill, and you get true miles per gallon, the metric L/100km equivalent, and, if you add a fuel price, the cost of each mile. Measuring real fuel economy reveals things a factory rating cannot. It shows how your commute, your right foot, and your maintenance habits affect efficiency, and it flags problems early: a sudden drop in MPG can signal underinflated tyres, a dragging brake, or a fouled sensor long before a warning light appears. Tracking it tank after tank turns a vague sense of thirst into hard data. The method is straightforward and reliable. Fill the tank, reset the trip meter, drive normally, then refill and record both the miles and the gallons added. Dividing distance by fuel gives MPG, and the calculator handles the metric conversion using the standard 235.215 factor so you can compare against European ratings. Doing this over several tanks smooths out the noise and produces a dependable picture of how your vehicle really performs.
MPG = miles ÷ gallons · L/100km = 235.215 ÷ MPG
Miles per gallon is simply the distance covered divided by the fuel consumed, giving the average reach of each gallon over the tank you measured. The metric equivalent inverts the idea, reporting litres needed to travel 100 kilometres, so the fixed factor 235.215 converts between the two. If you add a fuel price, dividing it by MPG yields the fuel cost of a single mile.
Source:U.S. EPA fuel economy
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter miles driven and gallons used.
- 2
Adjust the options
Adjust fuel price (optional) if they apply — sensible defaults are already set.
- 3
Read your result
Fuel economy updates instantly as you type — no button to press.
Frequently asked questions
How do I measure miles and gallons accurately?
Fill the tank completely and reset your trip odometer. Drive as you normally would, then return to the same pump and fill up again to the first click. The trip odometer shows miles driven, and the pump shows the gallons added to refill. Using the same pump and fill level each time keeps the measurement consistent, which matters far more than any single tank's exact reading.
What is a good MPG figure?
It depends heavily on the vehicle class. A compact hybrid may exceed 50 MPG, an efficient sedan sits around 30 to 40, while large trucks and SUVs often fall between 15 and 25. Rather than chasing a universal target, track your own vehicle over time and watch for changes. A steady figure is healthy; a falling one usually points to a maintenance issue worth investigating.
How does MPG relate to L/100km?
They describe the same efficiency from opposite directions. MPG measures distance per unit of fuel, so higher is better, while L/100km measures fuel per fixed distance, so lower is better. Because the relationship is reciprocal rather than linear, you convert with the fixed factor 235.215 divided by MPG. This calculator shows both, which is handy when comparing a US-rated car with a European specification.
Why does my MPG change from tank to tank?
Fuel economy responds to how and where you drive. Cold weather, short trips, heavy traffic, hills, roof racks, extra cargo, and aggressive acceleration all lower MPG, while steady highway cruising raises it. Tyre pressure and engine condition matter too. Because of this variation, a single tank can mislead. Averaging several consecutive tanks gives a much more reliable picture of your true fuel economy.
Can I calculate cost per mile here too?
Yes. The fuel price field is optional, but if you enter the price you paid per gallon, the calculator divides it by your MPG to show the fuel cost of every mile you drive. That per-mile figure is useful for budgeting, comparing vehicles, or setting mileage reimbursement rates. Leave the price blank and the tool simply reports MPG and the L/100km equivalent without a cost.